A bodybuilder is in training and performs curls with a 10-kg barbell to strengthen her biceps muscle.

Question:

A bodybuilder is in training and performs curls with a 10-kg barbell to strengthen her biceps muscle. At the top of the stroke, her arm is configured as in Figure P8.79, with her forearm at 35° with respect to the horizontal. Approximate her forearm and hand as a uniform rod of mass 1.4 kg and length 32 cm (from pivot point at the elbow to center of barbell). The biceps muscle is attached 3.1 cm from the pivot point at the elbow joint and produces a force that is directed 85° away from the forearm. What force must the biceps muscle exert to keep the weight at its current position?

Figure P8.79